Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

47.4 BENDING

 

· After basic shearing operation, we can bend a part to give it some shape.

 

· Bending parts depends upon material properties at the location of the bend.

 

· Some of the things that may/do occur in bends,

  1. - material at the outer bend radius undergoes tensile plastic deformation
  2. - material at the inner bend radius undergoes compressive plastic deformation
  3. - the width (along the bend axis) will reduce in length based on poissons ratio
  4. - if the bend radius is too small the plastic deformation at the outside of the bend will result in fracture.

 

· The basic calculations for a bend radius are shown below,

 

 

· The strain on the outermost fibers of the bend is,

 

 

· After sheet metal is bent it will tend to spring back to a lesser angle. The following formula relates bend radius before and after release.

 

 

· There are a variety of methods for springback compensating,

  1. - trail and error to over bend
  2. - calculated over bend
  3. - special punch/die designs

 

· The maximum bending forces may be calculated using the relationship below,

 

 

· Press Brakes a small presses that will bend a sheet metal piece over several feet.

 

· Some other operations done to sheet metal parts,

  1. beading - the edges of the sheet metal are bent back (in a rounded shape) to stiffen the edges and eliminate the sharp edge.
  2. flanges - a hole can be formed by punching through, and a lip (the flange) remains about the edge of the hole
  3. Hemming - like a bead, but the edge is bent back as a flat.
  4. Roll Forming - Bends can be made along long axes by using rollers.

 

· When planning to bend a piece, car must be take not to punch holes too close to the bend.

 

 

· Quality problems that occur in rolling are,

  1. flatness
  2. twist
  3. straightness